Analysis of memory modulation by conditioned stimuli.

Conditioned stimuli (CS) have multiple psychological functions that can potentially contribute to their effect on memory formation. It is generally believed that CS-induced memory modulation is primarily due to conditioned emotional responses, however, well-learned CSs not only generate the appropriate behavioral and physiological reactions required to best respond to an upcoming unconditioned stimulus (US), but they also serve as signals that the US is about to occur. Therefore, it is possible that CSs can impact memory consolidation even when their ability to elicit conditioned emotional arousal is significantly reduced. To test this, male Sprague-Dawley rats trained on a signaled active avoidance task were divided into "Avoider" and "Non-Avoider" subgroups on the basis of percentage avoidance after 6 d of training. Subgroup differences in responding to the CS complex were maintained during a test carried out in the absence of the US. Moreover, the subgroups displayed significant differences in stress-induced analgesia (hot-plate test) immediately after this test, suggesting significant subgroup differences in conditioned emotionality. Importantly, using the spontaneous object recognition task, it was found that immediate post-sample exposure to the avoidance CS complex had a similar enhancing effect on object memory in the two subgroups. Therefore, to our knowledge, this is the first study to demonstrate that a significant conditioned emotional response is not necessary for the action of a predictive CS on modulation of memory consolidation.

Enhancement of memory consolidation by an avoidance conditioned stimulus: Modulation by the D3 receptor.

Conditioned stimuli (CS) paired with foot-shock can enhance memory consolidation. Because the dopamine D3 receptor (D3R) has been implicated in mediating various responses to CSs, the current study explored its potential role in modulation of memory consolidation by an avoidance CS. Male Sprague-Dawley rats trained to avoid foot-shocks in a two-way signalled active avoidance task (8 sessions, 30 trials per session, 0.8 mA foot-shock) were pre-treated with the D3R antagonist NGB-2904 (Vehicle, 0.1 or 5 mg/kg) and exposed to the CS immediately after the sample phase of an object recognition memory task. Discrimination ratios were assessed 72 h later. Immediate, but not delayed (6 h), post-sample exposure to the CS enhanced object recognition memory and this effect was blocked by NGB-2904. Control experiments with the beta-noradrenergic receptor antagonist propranolol (10 or 20 mg/kg) and D2R antagonist pimozide (0.2 or 0.6 mg/kg) indicated that NGB-2904 targeted post-training memory consolidation. Exploring the pharmacological selectivity of the NGB-2904 effect, it was found that: 1) 5 mg/kg NGB-2904 blocked conditioned memory modulation produced by post-sample exposure to a "weak" CS (one day of avoidance training) and concurrent stimulation of catecholamine activity by 10 mg/kg bupropion; and 2) post-sample exposure to a "weak" CS and concurrent administration of the D3R agonist 7-OH-DPAT (1 mg/kg) enhanced consolidation of object memory. Finally, because 5 mg/kg NGB-2904 had no effect on modulation by avoidance training in the presence of foot-shocks, the findings herein support the hypothesis that the D3R plays an important role in modulation of memory consolidation by CSs.

Conditioned anti-immobility by ketamine: A comparison to escitalopram and bupropion.

This study was designed to explore the clinical belief that "set and setting" play an important role in favorable responses to psychedelic agents such as ketamine (KET). In fact, there is evidence in animals that the antidepressant effect of this drug may involve drug-environment interactions in which a context paired with its effects acquires the ability to influence behavior. Therefore, it was investigated in male Sprague-Dawley rats whether exposure to a context paired with the effects of KET, or with the effects of the common antidepressant medications bupropion (BUP) and escitalopram (ESC), could produce an antidepressant-like conditioned response. In Experiment 1, subjects received saline in a vehicle-paired context (denoted as CS-), and 0, 10, or 20 mg/kg KET, 10 mg/kg ESC, or 10 mg/kg BUP in a drug-paired context (denoted as CS +), on 10 alternating days (5 pairings with each context). The rats were then exposed drug free to the CS- and CS + prior to the assessment of immobility in the forced-swimming test. Experiment 2 assessed approach/avoidance responses induced by the CS- and CS + in a place-conditioning test. It was found that exposure to the KET CS + significantly reduced immobility without affecting general locomotor activity in comparison to the SAL CS + and the BUP CS +, but not the ESC CS+. Moreover, no group differences were observed in the place-conditioning test, indicating that the anti-immobility effect of the KET CS + was likely not influenced by a conditioned incentive or aversive state. Together, these data suggest that a KET-paired context can elicit a conditioned antidepressant-like response, which may be a mechanism involved in its sustained antidepressant clinical action. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Double dissociation of perirhinal nicotinic acetylcholine receptors and dopamine D2 receptors in modulation of object memory consolidation by nicotine, cocaine and their conditioned stimuli.

There are indications that drug conditioned stimuli (CS) may activate neurochemical systems of memory modulation that are activated by the drugs themselves. To directly test this hypothesis, a cholinergic nicotinic receptor antagonist (mecamylamine; MEC: 0, 10 or 30 µg/side) and a dopamine D2 receptor antagonist (l-741,626: 0, 0.63, 2.5 µg/side) were infused in the perirhinal cortex (PRh) to block modulation of object recognition memory consolidation induced by 0.4 mg/kg nicotine, 20 mg/kg cocaine, or their CSs. To establish these CSs, male Sprague-Dawley rats were confined for 2 h in a chamber, the CS+, after injections of 0.4 mg/kg nicotine, or 20 mg/kg cocaine, and in another chamber, the CS-, after injections of vehicle. This was repeated over 10 days (5 drug/CS+ and 5 vehicle/CS- pairings in total). It was found that the memory enhancing action of post-sample nicotine was blocked by intra-PRh infusions of both MEC doses, and 30 µg/side MEC also blocked the memory enhancing action of the nicotine CS. Interestingly, intra-PRh MEC did not block the memory enhancing effect of cocaine, nor that of the cocaine CS. In contrast, the memory enhancing action of post-sample cocaine administration was blocked by both l-741,626 doses, and 2.5 µg/side also blocked the effect of the cocaine CS, but not the memory effects of nicotine or of the nicotine CS. This functional double dissociation strongly indicates that drug CSs modulate memory consolidation by activating neural systems that are activated by the drugs themselves.

Atrophy of S6K1(-/-) skeletal muscle cells reveals distinct mTOR effectors for cell cycle and size control.

The mammalian target of rapamycin (mTOR) and Akt proteins regulate various steps of muscle development and growth, but the physiological relevance and the downstream effectors are under investigation. Here we show that S6 kinase 1 (S6K1), a protein kinase activated by nutrients and insulin-like growth factors (IGFs), is essential for the control of muscle cytoplasmic volume by Akt and mTOR. Deletion of S6K1 does not affect myoblast cell proliferation but reduces myoblast size to the same extent as that observed with mTOR inhibition by rapamycin. In the differentiated state, S6K1(-/-) myotubes have a normal number of nuclei but are smaller, and their hypertrophic response to IGF1, nutrients and membrane-targeted Akt is blunted. These growth defects reveal that mTOR requires distinct effectors for the control of muscle cell cycle and size, potentially opening new avenues of therapeutic intervention against neoplasia or muscle atrophy.

Constitutively active Akt1 expression in mouse pancreas requires S6 kinase 1 for insulinoma formation.

Factors that promote pancreatic beta cell growth and function are potential therapeutic targets for diabetes mellitus. In mice, genetic experiments suggest that signaling cascades initiated by insulin and IGFs positively regulate beta cell mass and insulin secretion. Akt and S6 kinase (S6K) family members are activated as part of these signaling cascades, but how the interplay between these proteins controls beta cell growth and function has not been determined. Here, we found that although transgenic mice overexpressing the constitutively active form of Akt1 under the rat insulin promoter (RIP-MyrAkt1 mice) had enlarged beta cells and high plasma insulin levels, leading to improved glucose tolerance, a substantial proportion of the mice developed insulinomas later in life, which caused decreased viability. This oncogenic transformation tightly correlated with nuclear exclusion of the tumor suppressor PTEN. To address the role of the mammalian target of rapamycin (mTOR) substrate S6K1 in the MyrAkt1-mediated phenotype, we crossed RIP-MyrAkt1 and S6K1-deficient mice. The resulting mice displayed reduced insulinemia and glycemia compared with RIP-MyrAkt1 mice due to a combined effect of improved insulin secretion and insulin sensitivity. Importantly, although the increase in beta cell size in RIP-MyrAkt1 mice was not affected by S6K1 deficiency, the hyperplastic transformation required S6K1. Our results therefore identify S6K1 as a critical element for MyrAkt1-induced tumor formation and suggest that it may represent a useful target for anticancer therapy downstream of mTOR.

Impact of impaired glucose metabolism on responses to a psychophysical stressor: modulation by ketamine.

RATIONALE: There is evidence that hypoglycemia, a metabolic stressor, can negatively impact mood and motivation, and can interact with other stressors to potentiate their effects on behavior and physiology. OBJECTIVES/METHODS: The current study in male Sprague-Dawley rats explored the interaction between impaired glucose metabolism induced by 0, 200, or 300 mg/kg 2-deoxy-D-glucose (2-DG) and a psychophysical stressor induced by forced swimming stress (FSS; 6 sessions, 10 min/session). The endpoints of interest were blood glucose levels, progressive behavioral immobility, and saccharin preference (2-bottle choice test). Furthermore, it was investigated whether pre-treatment with 0, 10, or 20 mg/kg ketamine could modify the interaction between 2-DG and FSS on these endpoints. RESULTS: It was found that 2-DG increased blood glucose levels equally in all experimental groups, accelerated the immobile response to FSS, and suppressed saccharin preference 1 week following termination of stress exposure. As well, pre-treatment with ketamine blocked the effects of combined 2-DG and FSS on immobility and saccharin preference without affecting blood glucose levels and produced an anti-immobility effect that was observed during a drug-free test swim 1 week following administration. CONCLUSIONS: Overall, these findings demonstrate that impaired glucose metabolism can potentiate the effects of a psychophysical stressor, and that this interaction can be modulated pharmacologically by ketamine.

Memory enhancing effects of nicotine, cocaine, and their conditioned stimuli; effects of beta-adrenergic and dopamine D2 receptor antagonists.

BACKGROUND: There is evidence that post-training exposure to nicotine, cocaine, and their conditioned stimuli (CS), enhance memory consolidation in rats. The present study assessed the effects of blocking noradrenergic and dopaminergic receptors on nicotine and cocaine unconditioned and conditioned memory modulation. METHODS: Males Sprague-Dawley rats tested on the spontaneous object recognition task received post-sample exposure to 0.4 mg/kg nicotine, 20 mg/kg cocaine, or their CSs, in combination with 5-10 mg/kg propranolol (PRO; beta-adrenergic antagonist) or 0.2-0.6 mg/kg pimozide (PIM; dopamine D2 receptor antagonist). The CSs were established by confining rats in a chamber (the CS +) after injections of 0.4 mg/kg nicotine, or 20 mg/kg cocaine, for 2 h and in another chamber (the CS -) after injections of vehicle, repeated over 10 days (5 drug/CS + and 5 vehicle/CS - pairings in total). Object memory was tested 72 h post sample in drug-free animals. RESULTS: Co-administration of PRO or PIM blocked the memory-enhancing effects of post-training injections of nicotine, cocaine, and, importantly, exposure to their CSs. CONCLUSIONS: These data suggest that nicotine, cocaine as well as their conditioned stimuli share actions on overlapping noradrenergic and dopaminergic systems to modulate memory consolidation.

Effects of inescapable stress on responses to social incentive stimuli and modulation by escitalopram.

RATIONALE: Stress is a well-known risk factor for anhedonia, and its impacts on social reward functions may be mitigated by its controllability. Moreover, there are questions about the effectiveness of selective serotonin reuptake inhibitors (SSRIs) on improving social hedonic functioning deficits characteristic of major depression. OBJECTIVES: The current study in male Sprague-Dawley rats investigated the effects of uncontrollable stress on responses to social incentive stimuli and possible modulation by the SSRI escitalopram (ESC). METHODS: The effects of inescapable foot-shocks on preferential responses to a conspecific, and to a compartment that was previously paired with the presence of a conspecific, were assessed in a Y-apparatus in rats that received 0, 5, or 10 mg/kg ESC. RESULTS: Although inescapable foot-shock exposure did not significantly alter the investigation of the conspecific, it did impair the response to the social-paired compartment and, importantly, this impairment was reversed by ESC. CONCLUSION: These results indicate that psychophysical stress can negatively impact reactivity to learned social rewards and that SSRI administration can have positive therapeutic effects.

Effects of high fructose corn syrup on ethanol self-administration in rats.

OBJECTIVE: The addition of sweeteners to alcoholic beverages is thought to facilitate heavy alcohol consumption, and this may be of particular concern when the additive is high fructose corn syrup (HFCS). METHODS: Four experiments in male Sprague-Dawley rats were performed to investigate whether the addition of 25% HFCS to ethanol (5%, 10%, and 20% v/v ethanol) would alter its intraoral operant self-administration, palatability, and sensitivity to food deprivation stress. RESULTS: As anticipated, HFCS drastically increased ethanol intake, and this effect appeared driven by its caloric value. Importantly, HFCS increased the persistence of operant responding following extinction in animals trained to self-administer the combination, and the addition of HFCS to ethanol changed subsequent responses to ethanol, including increased palatability and intake. CONCLUSIONS: These results in rats suggest that the addition of HFCS to the list of ingredients in sweetened alcoholic beverages could play a significant role in the harmful consumption of ethanol-containing beverages.

Reverse translation of major depressive disorder symptoms: A framework for the behavioural phenotyping of putative biomarkers.

BACKGROUND: Reverse translating putative biomarkers of depression from patients to animals is complex because Major Depressive Disorder (MDD) is a highly heterogenous condition. This review proposes an approach to reverse translation based on relating relevant bio-behavioural functions in laboratory rodents to MDD symptoms. METHODS: This systematic review outlines symptom clusters assessed by psychometric tests of MDD and antidepressant treatment response including the Montgomery-Åsberg Depression Rating Scale, the Hamilton Depression Rating Scale, and the Beck Depression Inventory. Symptoms were related to relevant behavioural assays in laboratory rodents. RESULTS: The resulting battery of tests includes passive coping, anxiety-like behaviours, sleep, caloric intake, cognition, psychomotor functions, hedonic reactivity and aversive learning. These assays are discussed alongside relevant clinical symptoms of MDD, providing a framework through which reverse translation of a biomarker can be interpreted. LIMITATIONS: Certain aspects of MDD may not be quantified by tests in laboratory rodents, and their biological significance may not always be of clinical relevance. CONCLUSIONS: Using this reverse translation approach, it is possible to clarify the functional significance of a putative biomarker in rodents and hence translate its contribution to specific clinical symptoms, or clusters of symptoms.

Effective lead selection for improved protein production in Aspergillus niger based on integrated genomics.

The filamentous fungus Aspergillus niger is widely exploited for industrial production of enzymes and organic acids. An integrated genomics approach was developed to determine cellular responses of A. niger to protein production in well-controlled fermentations. Different protein extraction methods in combination with automated sample processing and protein identification allowed quantitative analysis of 898 proteins. Three different enzyme overproducing strains were compared to their isogenic fungal host strains. Clear differences in response to the amount and nature of the overproduced enzymes were observed. The corresponding genes of the differentially expressed proteins were studied using transcriptomics. Genes that were up-regulated both at the proteome and transcriptome level were selected as leads for generic strain improvement. Up-regulated proteins included proteins involved in carbon and nitrogen metabolism as well as (oxidative) stress response, and proteins involved in protein folding and endoplasmic reticulum-associated degradation (ERAD). Reduction of protein degradation through the removal of the ERAD factor doaA combined with overexpression of the oligosaccharyl transferase sttC in A. niger overproducing beta-glucuronidase (GUS) strains indeed resulted in a small increase in GUS expression.

Effects of combined escitalopram and aripiprazole in rats: role of the 5-HT1a receptor.

RATIONALE: Pre-clinical and clinical studies have suggested that the antidepressant efficacy of escitalopram (ESC) can be augmented by co-administration of aripiprazole (ARI). OBJECTIVE: To establish if the effects of ESC + ARI can be altered by modulating the 5-HT1a receptor. METHODS: Sprague-Dawley male rats received ESC + ARI (10 and 2 mg/kg/day, respectively, via osmotic or by cumulative injections), as well as the 5-HT1a antagonist WAY-100635 (WAY; 0.01-1 mg/kg) and the 5-HT1a agonist 8-OH-DPAT (DPAT; 0.3-1 mg/kg) prior to testing in locomotion chambers and in the forced swim test (FST). Expression of the 5-HT1a receptor mRNA in the dorsal raphe nucleus, hippocampus, septum, and entorhinal cortex was also assessed. RESULTS: WAY generally synergized, while DPAT antagonized, the effect of ESC + ARI on motor activity. All groups showed significantly lower 5-HT1a mRNA in the dorsal raphe nucleus. In the hippocampus, ESC + ARI and WAY + ESC + ARI groups displayed equivalent elevations of 5-HT1a mRNA, but this was not observed in groups that received DPAT + ESC + ARI. Finally, the addition of ARI to ESC augmented the effect that ESC alone had on reducing immobility in the FST. Importantly, WAY antagonized this effect, while DPAT had no consequences. CONCLUSIONS: Taken together, these results in rats indicate that the 5-HT1a receptor is involved in the behavioral and brain region-specific mRNA effects of ESC + ARI.

Correction to: Effects of combined escitalopram and aripiprazole in rats: role of the 5-HT1a receptor.

After publication of this paper, the authors determined an error in Fig. 3. Below is the correct Fig. 3.

A study of limbic brain derived neurotrophic factor gene expression in male Sprague-Dawley rats trained on a learned helplessness task.

BACKGROUND: Brain derived neurotrophic factor (BDNF) has been linked to the etiology and pathology of Major Depressive Disorder (MDD). Here, the relationship between learned helplessness (LH), a cognitive/motivational state relevant to MDD, and BDNF mRNA in various limbic regions, was investigated. METHODS: In Sprague-Dawley male rats, LH was induced by escape training, using a triadic design of stressor controllability involving exposure to no shocks (NS), escapable shocks (ES) or yoked inescapable shocks (IES). LH was subsequently assessed in an active avoidance task, and levels of BDNF mRNA in limbic brain regions were compared across the triad following testing. RESULTS: Although the IES group displayed greater LH, BDNF mRNA levels were lower in the hippocampus and higher in the nucleus accumbens of both IES and ES groups. In contrast, BDNF mRNA in the basolateral amygdala was elevated only in rats exposed to IES. CONCLUSION: These results suggest that the inability to control an aversive stimulus can lead to a LH behavioural phenotype that is associated with region-specific alterations of BDNF gene expression in limbic nuclei.

Genome of a Gut Strain of Bacillus subtilis.

Bacillus subtilis is a Gram-positive, rod-shaped, spore-forming bacterium. We present the genome sequence of an undomesticated strain, BSP1, isolated from poultry. The sequence of the BSP1 genome supports the view that B. subtilis has a biphasic lifestyle, cycling between the soil and the animal gastrointestinal tract, and it provides molecular-level insight into the adaptation of B. subtilis to life under laboratory conditions.